I. FIELD OF THE INVENTION
The present invention relates to protective devices for suppressing short duration, high energy impulses, such as lightning strikes, which may occur along coaxial cables or other HF, VHF or UHF transmission lines. More particularly, the invention relates to the use of a discharge device in combination with connectors for being inserted in series with the transmission line.
II. DESCRIPTION OF THE PRIOR ART
The use of vacuum tubes in prior radio frequency transmitting and receiving equipment made them somewhat tolerant to nearby lightning strikes since the breakdown voltage of the tubes was relatively high and since the tubes would typically not be damaged unless there was a direct lightning strike on the antenna or the feedline. On the other hand, recent advances in solid state design technology have allowed transistors to replace tubes in most applications. The problems of surge protection or lightning strikes for transistorized receivers or transmitters is especially troublesome in view of the low breakdown voltages for typical solid state devices. Once this low breakdown voltage has been exceeded, the solid state device is no longer operative and must be replaced.
The cost of the lightning or surge protection has become more economical in view of the large cost of repairing this equipment. This cost factor becomes even more economical when the lightning or surge protection device can withstand multiple lightning strikes of reasonable intensity without the necessity of replacing the protective device or without distruction of any equipment attached thereto. However, these economies of lightning protection are not acceptable if the performance of the system in which the lightning protection device is used is degraded by the insertion of the protection device. Transmitting systems are of the greatest interest in this regard since the insertion loss and VSWR along the transmission line are somewhat critical at VHF and UHF frequencies.
In contrast to the prior art devices that did not propertly match the impedance of the transmission line, the present invention relates to a connector of the type which may be inserted into a length of coaxial radio frequency cable, or other HF, VHF or UHF transmission line, for controlling and dissipating the surge energy (such as lightning) traveling from the antenna side toward the receiver/transmitter side, while not presenting a high VSWR or insertion loss when viewed from the transmitter end toward the antenna end of the line. The capacitance of the discharge device used in the circuit, and other stray or distributed capacitances, are cuased to interact with distributed inductive reactance so that the characteristic impedance of the connector, when viewed as a lumped element circuit, will correspond to the characteristic impedance of the transmission line. Thus, the connector will be transparent to the transmitted RF signal, but will be effective in dissipating or shunting the electrical impulse traveling down the line.